A heat sensitive paper widely known to the art comprises a leuco dye and a color developing agent and can produce color by the application of heat from a heating element, such as a thermal head. The heat sensitive paper is generally used for a recording material for a facsimile, a printer etc., because it is produced at low cost and necessitates a relatively small apparatus which is easily treated by an operator.
On the other hand, multiple color or full color recording has been recently required together with the extended utility of recording apparatus. The full color requirement generally uses electrostatic recording using laser light, ink-jet printing, heat transfer film and the like, but heat sensitive paper has not been employed. A full color recording material using the characteristics of heat sensitive paper wherein a multiple color image will be obtained by changing the heat energy applied by a thermal head is also desired.
For this purpose, an attempt is considered that the developing color tone is changed in concord with the thermal energy applied from a thermal head, using a combination of leuco dye and developing agent. For example, a combination of a low-temperature color-developing layer and a high-temperature color-developing layer that create different color tones is formed and changes developing color tone by change of the thermal energy. In the method, however, the high-temperature color developing layer is developed at a high temperature which is also developing the low-temperature color-developing layer. Thus, the developed color at the high temperature must be a mixed color. It is difficult to obtain the original color tone of each leuco dye originally has.
In order to improve the above defect, it is proposed that a color eraser which erases the developed color of the low-temperature color-developing layer at the high temperature is used to give the developed color of the high-temperature color-developing layer while erasing the color of the low-temperature color-developing layer. The heat sensitive multiple color recording materials using the color eraser are disclosed in Japanese Kokai Publications, Sho 55 (1980)-7449, Sho 55(1980)-7450, Hei 5(1993)-185715, Hei 5(1993)-193254 and Hei 5(1993)-201127 and Japanese Kokoku Publication Hei 4(1992)-32752; or U.S. Pat. No. 4,620,204. However, it is still difficult to inhibit color mixture and it is very hard to keep the developed color tones completely separated from each other. It is also very difficult to obtain heat sensitive multiple color recording materials of three or more colors. In addition, the developed color is gradually color-changed or discolored by the function of the color eraser when time goes on.